Multi-user multi input multi output (MIMO) communication systems allow a plurality of users to access the same resource simultaneously. Allowing a plurality of users to access the same resource simultaneously requires that the MIMO communication system have multiple antennas at the transmitter and at the receiver. However, to accommodate the increased number of users without impacting throughput, a number of techniques are used.
One technique, downlink pre-equalization utilizes linear precoding at the transmitter for interference suppression to increase the number of users, but suffers from the limitation of unconstrained transmitted energy on the multiple antennas. Another technique, dirty paper coding (DPC) utilizes non-linear precoding at the transmitter for interference suppression to increase the number of users. DPC constrains the transmitted energy on the multiple antennas by applying constellation mapping, such as replicated constellation mapping. Constellation mapping means to encode the data to be transmitted as a lattice. In replicated constellation mapping, an initial constellation is replicated to produce replicated constellations. An image of the symbol to be transmitted from the initial constellation is selected from the replicated constellations and transmitted from the transmitter. The image of the symbol in the replicated constellations is then received at the receiver. The receiver applies a modulo function to recover a corresponding point to the received signal. However, since the replicated constellation does not address the impact of noise on the modulo function, errors are caused in the detection of the encoded signal. Thus, even existing DPC techniques are deficient.
Accordingly, there exists a need for a new method for encoding a modulated signal in a communication system.
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Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.